1. Field of the Invention
The present invention relates to a frequency converter according to the preamble of Claim 1, in particular for devices used at construction sites.
2. Description of the Related Art
At construction sites, as a rule the power supplied is line current having a frequency of 50 Hz and a voltage of 230 V (sometimes also 400 V). The frequency converter to which the present invention relates converts this power available at the site into, for example, a three-phase current having a frequency of 200 Hz and a protective extra-low voltage of 42 V, the protective extra-low voltage being required in order to protect the operator from electrical risk, e.g. in a wet environment.
In known devices of this type, an isolating transformer and a converter circuit board are used that, due to their power loss, release heat that has to be dissipated. This is achieved through the use of heat sinks having a sufficiently large cooling surface, a sufficiently large housing, or overdimensioning of the isolating transformer. These heat dissipation measures are cost-intensive and result in greater weight. The known devices can have external cooling fins that can accumulate dirt and concrete over time, which has an increasingly adverse effect on the heat dissipation.
From EP-A-0 854 565, a frequency converter is known that has a converter device surrounded by a housing for converting an electrical current frequency. The housing has a converter receptacle that surrounds a board chamber for the converter device, as well as a housing segment, connected to the converter receptacle, that acts as a cooling area, inside which there are situated cooling air ducts and a fan suited for conveying cooling air through the cooling air ducts.